In recent years, as the advancement of electronic equipment has been made, more electronic components are used in a chip form and it has become the industry trend to build electronic circuits by employing surface mount technology.
To cope with this trend, not only excellent solderability is required of the terminals of chip components but also high heat resistance to withstand the temperatures of two hundreds and several tens of degrees for a protracted period has been required of the chip components themselves.
In the area of electrolytic capacitors that have been inherently vulnerable in terms of heat resistance, chip type products for a surface mounting application have become available as the advancement in materials and technologies has been made recently. An example of such surface mountable electrolytic capacitors is a solid electrolytic capacitor as shown in FIG. 8, which is formed by molding an interior capacitor element together with lead frames 21 and 22, which also serve as terminals, with an encapsulating resin 23.
However, the foregoing conventional solid electrolytic capacitor has a problem of degradation of the interior capacitor element caused by infiltration of oxygen and moisture into the inside of the resin from outside that takes place at the time of surface mounting of the chip capacitor. The cause of the above infiltration can be further attributed to the following two points:
(1) The tin or solder layer on the surface of the lead frame melts due to the heat applied at the time of surface mounting of the chip capacitor and thereby a gap is created between the encapsulating resin and the lead frame.
(2) Due to the differential in thermal expansion coefficient between the metal forming the lead frame (usually iron) and the encapsulating resin, a gap is formed between the encapsulating resin and the lead frame.
The object of the present invention is to solve the foregoing problem involved with the conventional solid electrolytic capacitor, thereby making it possible to supply a solid electrolytic capacitor exhibiting high reliability even when a thermal shock is imposed to the electrolytic capacitor at the time of surface mounting.